The purpose of this proposal is to develop rhesus cytomegalovirus (RhCMV) as model system for studying human cytomegalovirus pathogenesis. Specifically, we will be studying the growth determinants of RhCMV in monocyte-derived macrophages (also infected by human immunodeficiency virus or simian immunodeficiency virus), by using a transposon mutagenesis system and bacterial artificial chromosome (BAC) technology.